This invention relates to an nematic liquid crystal composition which exhibits positive dielectric anisotropy having no absorption in the visible region. More particularly, the invention relates to a nematic liquid crystal composition, including at least two liquid crystal compounds having a cyano group, a compound having an alkoxy group and at least one liquid crystal compound having an n-alkyl group, which is suitable for forming a host liquid crystal for a guest-host type liquid crystal display device.
Liquid crystal displays utilizing the guest-host effect are known. They comprise a dielectrically anisotropic nematic liquid crystal wherein at least one dichroic dye is dissolved to provide a differently colored display upon applying a voltage across the liquid crystal composition. The field-effect type liquid crystal display device provides a display in desired colors if an appropriate dichroic dye is employed. A display substantially of the same quality may be obtained, irrespective of the angle of vision, at low voltage and with low power consumption. Generally speaking, the compositions provide a bright display since they do not require polarizing plates, and if a polarizing plate is used only one is required.
It is common practice to employ a twisted nematic liquid crystal as the host liquid crystal in a guest-host type liquid crystal display. However, it is important to use a host liquid crystal in which the characteristics of the dichroic dye as a guest significantly improve the quality of the display. More specifically, it is important to use a liquid crystal which satisfies the following requirements:
1. high solubility of the dye in the liquid crystal;
2. highly ordered arrangement of the dye;
3. no absorption in the visible region;
4. high environmental resistance and stability;
5. maintenance of the nematic phase over a wide temperature range, including ordinary temperature;
6. high dielectric anisotropy and suitability for low voltage driving; and
7. low viscositiy.
Accordingly, it is desirable to provide a liquid crystal composition which meets the foregoing requirements (1) to (7) and is suitable as a host liquid crystal in a guest-host liquid crystal display. As a result of extensive research efforts, the inventor has discovered a liquid crystal composition which satisfies all of the above-noted requirements specified in (1) to (7).